Leaving the dark ages with AMIGA

TL;DR

AMIGA is a semi-analytic model that simulates the evolution of the intergalactic medium and galaxies from the dark ages, incorporating molecular cooling, Pop III stars, and ionization processes, with minimal free parameters.

Contribution

It introduces a grid-based interpolation approach for halo properties, reducing memory use and enabling high-redshift modeling, while including detailed feedback from Pop III stars.

Findings

Pop III stars set IGM metallicity and temperature.

Galaxy growth is regulated by black hole development.

Normal galaxy properties are insensitive to Pop III star details.

Abstract

We present an Analytic Model of Intergalactic-medium and GAlaxy evolution since the dark ages. AMIGA is in the spirit of the popular semi-analytic models of galaxy formation, although it does not use halo merger trees but interpolates halo properties in grids that are progressively built. This strategy is less memory-demanding and allows one to start the modeling at redshifts high enough and halo masses low enough to have trivial boundary conditions. The number of free parameters is minimized by making the causal connection between physical processes usually treated as independent from each other, which leads to more reliable predictions. But the strongest points of AMIGA are: i) the inclusion of molecular cooling and metal-poor, population III (Pop III) stars, with the most dramatic feedback, and ii) the accurate follow-up of the temperature and volume filling factor of neutral, singly, and doubly ionized regions, taking into account the distinct halo mass functions in those environments. We find the following general results. Massive Pop III stars determine the IGM metallicity and temperature, and the growth of spheroids and disks is self-regulated by that of massive black holes developed from the remnants of those stars. Yet, the properties of normal galaxies and active galactic nuclei appear to be quite insensitive to Pop III star properties owing to the much higher yield of ordinary stars compared to Pop III stars and the dramatic growth of MBHs when normal galaxies begin to develop, which cause the memory loss of the initial conditions.